1. Field
The invention is in the field of recording and playback apparatus for magnetic tape cassettes or the like.
2. State of the Art
Since the introduction of tape cassettes a number of years ago, the cassette format for magnetic tape has become very popular and a wide variety of equipment is available for recording and playing back tape cassettes and for playing pre-recorded monophonic and stereophonic tape cassettes. An important area of use for cassette equipment is in the recording and playback of the spoken word. This may be for educational purposes, such as tapes of lectures, conferences, readings of textbooks, etc., or for entertainment, such as the reading of plays and novels. Such tapes are usually monophonic and do not require high fidelity sound reproduction. The important considerations are the convenience of the cassette format and the amount of material that can be put onto a cassette.
Most cassette record and playback equipment available is designed to operate at one standard speed, and most pre-recorded cassettes are designed to be played at that one standard speed. Also, it is customary to divide the width of the magnetic tape in the cassette into four tracks, with two tracks being recorded or played simultaneously for each so-called "side" of the cassette. These two tracks are separately but simultaneously recorded or played back for stereophonic tapes, or are recorded or played back in common for monophonic tapes.
Since the size of the cassette limits the amount of tape that can be placed in it, there are two ways to increase the recording time of a single cassette without increasing the amount of tape. One way is to increase the number of tracks on the tape and another is to move the tape more slowly. One way to effectively increase the number of tracks on the tape when only monophonic recording and playback are necessary is to use each of the four tracks separately rather than using two of the tracks simultaneously. This means that twice as much information may be stored on the same amount of tape. By reducing the speed of the tape, a proportiately greater amount of material may be stored on the same amount of tape. For example, reducing the speed by one-half doubles the amount of material that can be recorded on the tape while reducing speed to one-quarter that of normal gives four times as much material on the same tape.
Although it sounds like a simple matter to increase the amount of material stored on a cassette tape, numerous problems arise in actually trying to do so.
The cassette track format has been standardized, so any record or playback apparatus that uses a different track arrangement is limited in material that can be used with the equipment unless it is adapted to record and play the standard cassettes as well. Problems have been encountered, however, in designing machines that can change track format so as to selectively use either a single track format or the two track format of the standard cassettes. Applicant is aware of one machine that will play back either a single track or the dual track of the standard cassette but will not record in such single track format. As far as applicant is aware, track format switching is not available in the prior art for both recording and playback.
The speed at which a tape passes the head in a tape record and playback apparatus has a significant effect on the frequency response obtainable for the recorded and played back signal. The standard cassette speed of 4.8 millimeters per second was chosen to give satisfactory high fidelity frequency response for the recorded and played back signals with state of the art tape and magnetic recording and playback heads while at the same time going as slowly as possible to give maximum information storage on the tape. Any reduction in tape speed reduces the frequency response by a like percentage. Cassette playback equipment operating at one half standard speed is currently in use by the U.S. Library of Congress for tape cassettes and playback equipment it supplies for use of the blind. These tapes generally use the spoken word (readings of novels, etc.) so high fidelity is not required. It has been suggested that the speed be reduced even further to one-quarter the normal speed, and some equipment has been modified on a limited basis to test this. However, such equipment has not had satisfactory sound quality to be a viable product in the market place. A major problem, in addition to frequency response, has been control and regulation of the motor at the reduced speed to eliminate variations in speed that can cause wow and flutter.